The present invention relates to the non-halogenated polyamide compositions, and in particular to such compositions that have flame retardant properties.
Polyamides such as nylon have a variety of commercial uses. One important use is as a resin for molding articles. It is often important for molded polyamide articles to have flame retardant properties. The means used in the past for achieving flame retardancy in polyamide compositions have presented various problems or shortcomings.
Incorporation of halogen compounds can improve flame retardancy, but does not offer the most environmentally friendly system. One problem for example is the reduction in mold life due to the corrosive nature of halogens. Non-halogenated flame retardant (NHFR) nylon compositions can be created by incorporating melamine cyanurate. NHFR nylon products prepared with a copolymer base resin have a high degree of toughness, but the copolymer causes the composition to have a longer set-up or cure time in molding processes. A fast set-up time is desired in molding processes in order to increase throughput and thereby reduce manufacturing cost. Lowering the relative viscosity (RV) of the base copolymer resin will reduce set-up time, but also diminishes the flame retardancy (as measured for example by the Underwriters"" Laboratories UL-V0 Vertical Flame Test).
A need exists for improved polyamide compositions that have both good flame retardancy properties and relatively fast set-up times in molding processes, while also having other desirable properties such as toughness.
One aspect of the present invention is a polyamide composition comprising (a) at least one polyamide other than nylon 2,2, or a copolymer of at least two polyamide repeating units, neither of which is nylon 2,2, (b) melamine cyanurate, and (c) a nucleating agent in an amount effective to cause nucleation of the polyamide of (a). In a preferred embodiment, the nucleating agent is nylon 2,2. The nylon 2,2 preferably is present in an amount between about 0.001% and about 0.1% by weight, more preferably in an amount between about 0.01% and about 0.05% by weight.
The polyamide of (a) can for example be nylon 6,6. As another example it can be a copolymer of nylon 6,6 and nylon 6. Preferably the polyamide has a relative viscosity (RV) of from about 40 to about 55. An RV in the range of about 44-50 is especially preferred.
The composition can further comprise one or more fillers, reinforcing agents, stabilizers, dyes, other flame retarding agents, mold-release agents, plasticizers, pigments, ultraviolet light absorption agents, antistatic agents, or lubricants.
Preferably the copolymer is from about 75-95% by weight of the composition, the melamine cyanurate is from about 1-15% by weight of the composition, and the nucleating agent (e.g. nylon 2,2) is from about 0.001-0.1% by weight of the composition. In a particularly preferred embodiment, the copolymer is from about 85-95% by weight of the composition, the melamine cyanurate is from about 5-10% by weight of the composition, and the nylon 2,2 is from about 0.01-0.05% by weight of the composition.
Another aspect of the present invention is a process for producing nucleated polyamide. The process comprises cooling a molten polyamide other than nylon 2,2 in the presence of (a) melamine cyanurate and (b) a nucleating agent in an amount effective to cause nucleation of the polyamide. In various embodiments of the process, the reactants and proportions can be as described above with respect to the composition.
The compositions of the present invention exhibit commercially desirable flame retardancy, toughness, and flow, yet also have relatively short set-up times in molding and thus reduced molding cycle times. In particular, compositions of the present invention can meet the Underwriters"" Labs UL-VO flame retardancy test while maintaining relatively short set-up times in molding operations. This improvement in molding cycle time increases manufacturing throughput and reduces unit cost.